The general trend in the recent progress of geomorphology is development of its dynamic aspects and transformation on the basis of the exact sciences data according to the system analysis requirements. The traditional geomorphology of the evolutionary stage provides conceptual models which are the first step of formalisation towards geomorphic systems development.
Morphostructures of Russian (East European) and West Siberian platform plains when analysed and compared with morphostructures of other platforms of the Earth strongly suggest that morphostructural features of the plains depend on the position of each plain in global system of of geotectures. The basement's age is concluded to be of secondary importance and should not be taken as a basis for the platform plains classification.
Discussions
Both topography and geomorphology study the surf ace of the Earth, and topographic and geomorphological models reflect two sides of the object- its continuity and discreteness. It manifests the transition from quantitative changes on the surface of the Earth to qualitative ones, which in turn reflects continuous and discrete character of lithodynamic flows. The geomorphological studies require reduction of the Earth surface to elementary units, the procedure being the basis of all subsequent data processing.
A precise wording is necessary to determine the «elementary morphological unit» (E. M. U.), so that everyone could establish it unambiguously. A simplest drainage area of a first order stream can be used as a unit of this kind. Such E. M. U. is the simplest cell of the hierarchic structure of the higher rank geomorphosystems.
Short communications
The morphostructures of the eastern Great Caucasus are analysed using the data of 'the space photoes interpretation. Morphostructural features as revealed from the space photoes permit to distinguish linear zones which delimit folded-block morphostructural steps of general Caucasian orientation as well as transversal block segments. The recent morphostructural framework of the region is established to result from folded-block-fault tectonics and horizontal displacements (large regional overthrusts) which account for complicated relief of the eastern Great Caucasus.
Accelerated fluvial erosion is pronounced locally around the Baikal Lake, in a relatively small Kuitunka drainage basin in particular. The area in question is covered with loess-like deposits. The comparison of cartographic materials of different years (including topographic maps of 1911 and 1973 years and a land use map of 1934 yr) permitted to estimate the gullies formation dynamics and to describe some special features of the erosion in the area. The gullies development appeared to change considerably in the course of time. At present the gullies' density tends to increase due to inception of new gullies and reactivation of old ones.
The present-day erosion rate has been estimated within mountain area of the northern slope of the Alai Ridge using two methods: 1) based on solid runoff data, and 2) based on sediments volume in the Abshirsai Lake. Total rate of erosion on the Alai Ridge slope amounts to 0.22 mm per year. The value calculated from the volume of the lake deposits is in reasonable agreement with data obtained by solid runoff measurements in the rivers near the lake.
The paper discusses independent methods of direct determination of age of the Pacific deep-sea trenches. The methods of trench dating are based on recognition of the classic triad: «structure - age – genesis» for trenches, which have the thrust-nappe structure, while the seduction hypothesis is unproved.
The trench dating methods are analyzed using an abstracted thrust-nappe trench model, earlier developed by the authors during the study of the Kuril and Japan trenches. The direct methods of trench dating include dating correlate sediments, correlate tectonic structures (allochthon, autochthon and related faults), scarps on trench slopes, and channel net (submarine canyons of the continental slope and abyssal channels of the Pacific sea floor). The Pacific trenches appeared to be not older than Early-Middle Pleistocene (0.5 to 1 mln years ago). The trench formation epoch coincides with the Pasadena phase of progeny and folding (by H. Stille) which has probably global display and is continued up to now.
Some new concepts are developed and terms are introduced concerning channel processes manifestation under conditions of confluent rivers interaction (within the area of river junction, in the lower reach of the tributary, in the zone of the tributary influence on the trunk stream etc.). Delta formation in the junctions appeared to be controlled by solid runoff and backwater phenomena. Specific conditions are required to form «fill-in» delta, programming delta or other morphological types of river junctions.
New data indicate the evolution of mountain river valleys to be complicated, not unidirectional, but partly inherited. Similarly to valleys of plains some of them contain buried alluvial horizon. Regularities of the buried alluvium distribution are controlled by neotectonic regime; individual regions differ in the heights interval within which the erosion proceeded during the Late Cenozoic. The buried alluvium conservation is due to some conditions of the subsequent evolution of the valley. The data obtained are of both theoretical and applied importance.
The Surkhob valley is a part of the zone of collision of Eurasian and Indian lithospheric plates. Due to tectonic compression in the Holocene a narrow highly shattered zone was formed (lengthwise morphostructural lineament of the 1st rank), associated with the Ghissar-Kokshaal deep-seated fault and the Vakhsh over thrust. The recent activity of the faults was tentatively evaluated. Late Holocene displacements along longitudinal and transversal thrusts are identified from the Surkhob terraces profiling. Geodetic system of the Garm test area is arranged according to morphostructural plan of the Surkhob valley which is controlled by the Ghissar- Kokshaal fault zone. Geomorphological data permit to delimit an area of highly contrast displacements in the frontal zone of the Vakhsh over thrust where the two fault zones interact.
Floodplains influence channel deformations 1) by sediments exchange between channel and floodplain in the course of the latter formation and also due to the floodplain's scarps erosion during floods. and 2) by the floodplain's and channel's streams interaction, In the latter case the shallows development is mostly affected, depending on the character of contact between the streams, on the river's hydrological regime, configuration and size of the floodplain's segments and their relief and vegetation. The floodplain impact on the shallows evolution is most pronounced on the rivers having broad meadow floodplain with troughs and islands, where floodplain and channel streams intercross during frequent floods. Besides, the influence is clearly seen in the river channel where meandering is restricted and floodplain's segments are arranged in staggered order. On the whole, floodplains facilitate formation of more complicated channel landforms.
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